Feedback between a wireless device and a base station is an invaluable mechanism for increasing the reliability and efficiency of a wireless communications network. Robust feedback mechanisms allow for a reliable communication link between a wireless device and a base station, while simultaneously minimizing the amount of power used to transmit signals between the two.
Some common feedback mechanisms for cellular communications networks include acknowledge/negative-acknowledge (ACK/NACK) messages and channel state information (CSI). ACK/NACK messages may be sent based on whether certain data was received by either a wireless device or a base station in the cellular communications network. ACK/NACK messages may be used to support downlink hybrid automatic repeat request (HARQ) error correction in the cellular communications network, which uses error-correcting coding to provide a more reliable communication between a base station and one or more wireless devices in the cellular communications network.
CSI refers to one or more properties of a communication link the cellular communications network. CSI may include a pre-coding matrix indicator (PMI), a rank indicator (RI), and a channel quality indicator (CQI), and may be used to support a downlink scheduling mechanism for resource allocation, link adaptation, the determination of pre-coding vectors, etc. The accuracy and frequency of CSI is critical to the downlink performance of the cellular communications network. Accurate CSI can be used by a base station to determine an appropriate pre-coding vector for transmit diversity, beam-forming, multiple-input/multiple-output (MIMO), etc.
In Long Term Evolution (LTE) cellular communications networks, advanced transmission schemes such as downlink multi-user MIMO and coordinated multipoint (CoMP) are used to increase system capacity and cell-edge performance. In addition, carrier aggregation provides more component carriers for a single wireless device to increase throughput of the device. While the use of advanced transmission schemes may improve the overall throughput of a cellular communications network, such transmission schemes often require additional feedback mechanisms in order to properly function.
Currently, feedback information is sent in uplink transmissions via a physical uplink control channel (PUCCH) and a physical uplink shared channel (PUSCH). For feedback information transmitted via the PUCCH, a periodic scheme is used wherein feedback information is sent in a predefined transmission time interval (TTI). Feedback information transmitted via PUSCH is also transmitted periodically.
Generally, uplink radio resources need to be partitioned between data transmission and wireless device feedback. In other words, there is a trade-off between the total throughput of a wireless device and the amount of feedback used in the cellular communications network. One solution to this problem is to quantize feedback information from a wireless device before transmitting it. While this reduces the number of bits of feedback information, it comes at the cost of reduced performance. The reduced performance, as a result of using quantized feedback, may render the network incapable of supporting the advanced transmission schemes offered in an LTE cellular communications network.
Accordingly, there is an ongoing need for additional bandwidth for feedback information in a cellular communications network without a reduction in the bandwidth allocated for user data.